It is known to use robots for assisting and performing surgery. FIG. 1 illustrates a typical surgical robot 100 which consists of a base 108, an arm 102, and an instrument 105. The base supports the robot, and is itself attached rigidly to, for example, the operating theatre floor, the operating theatre ceiling or a trolley. The arm extends between the base and the instrument. The arm is articulated by means of multiple flexible joints 103 along its length, which are used to locate the surgical instrument in a desired location relative to the patient. The surgical instrument is attached to the distal end 104 of the robot arm. The surgical instrument penetrates the body of the patient 101 at a port 107 so as to access the surgical site. At its distal end, the instrument comprises an end effector 106 for engaging in a medical procedure.
FIG. 2 illustrates a typical surgical instrument 200 for performing robotic laparoscopic surgery. The surgical instrument comprises a base 201 by means of which the surgical instrument connects to the robot arm. A shaft 202 extends between base 201 and articulation 203. Articulation 203 terminates in an end effector 204. In FIG. 2, a pair of serrated jaws are illustrated as the end effector 204. The articulation 203 permits the end effector 204 to move relative to the shaft 202. It is desirable for at least two degrees of freedom to be provided to the motion of the end effector 204 by means of the articulation.
FIG. 3 illustrates an example of a known surgical instrument 300 in which end effector 204 is permitted to move relative to shaft 202 by means of pitch joint 301 and two yaw joints 302. Joint 301 enables the end effector 204 to rotate about pitch axis 303. Joints 302 enable each jaw of the end effector 204 to rotate about yaw axis 304. The joints are driven by cables 306, 307 and 308. Pulley 305 is used to direct cables 307 and 308 from their passage over the pitch joint to the yaw joints. Pulley 305 is offset from the central axis of the articulation 203.
The external diameter of the shaft is 8 mm in order to accommodate the number, size and location of the internal elements of the articulated portion.
It is desirable to reduce the external diameter of the instrument in order to minimise the size of the incision through the skin of the patient and minimise disruption inside the patient's body. It is also desirable to minimise the weight of the surgical instrument so as to minimise the size and weight of the robot base and arm required to support the instrument, thereby enabling the robot as a whole to be more compact and hence occupy a smaller space in the operating theatre and be more moveable within the operating theatre.
In a typical laparoscopy operation, a surgeon utilises many instruments, and hence exchanges one instrument for another many times. It is therefore desirable to minimise the time taken and maximise the ease with which one instrument is detached from a robot arm and a different instrument is attached. Additionally, it is desirable to minimise the time taken in setting up the instrument ready for use once it has been attached to the robot arm.